Axial lead connector for implantable medical devices

ABSTRACT

An axial lead connector assembly for an implantable medical device (IMD) facilitates electrical connection between an implantable medical lead and circuitry contained within the housing of an IMD. A connector header defines an axial stack bore to receive an axial stack of in-line connector components. The connector components define a common lead bore to receive a proximal end of an implantable lead. The in-line stack of connector components may include seals, electrical connector elements, a strain relief, and a locking device, each of which defines a passage that forms part of the lead bore.

TECHNICAL FIELD

The invention relates to medical leads for implantable medical devices(IMDs) and, more particularly, to electrical connectors that facilitateelectrical coupling between the medical leads and circuitry of the IMD.

BACKGROUND

In the medical field, leads are used with a wide variety of medicaldevices. For example, leads are commonly used with implantablestimulators that provide electrical stimulation. Electrical stimulationmay be delivered to sacral, pudendal or other pelvic nerves within thepelvic floor of a patient to alleviate a variety of disorders such asurinary incontinence, fecal incontinence, constipation, sexualdysfunction, pelvic pain, or other pelvic floor disorders. Otherapplications include spinal cord stimulation, gastric stimulation anddeep brain stimulation. The electrical stimulation is delivered viaelectrodes disposed at or near the distal ends of one or more leads.Leads may also be used with implantable cardiac pacemakers that providetherapeutic stimulation to the heart by delivering pacing, cardioversionor defibrillation pulses. In that case, the leads may position theelectrodes with respect to various cardiac locations so that thepacemaker can deliver pulses to the appropriate locations. Leads mayalso be used for sensing purposes, or both sensing and stimulationpurposes.

One challenge in implementing medical leads in a medical device is theelectrical coupling between a lead and circuitry of the IMD. An IMDincludes a housing that houses an implantable pulse generator (IPG)containing circuitry, and a connector module that couples the lead tothe circuitry, either directly or via a lead extension. The connectormodule includes electrical contact structures for coupling the lead tocircuitry within the housing of the IMD so that therapeutic simulationcan be provided through the lead, or sensed conditions can be recordedby the circuitry. The connector module must ensure reliable electricalconnections between the IMD circuitry and the lead, while alsomaintaining a sufficient seal between the connector module and the leadto avoid ingress of body fluids into the housing, and the possibility ofelectric shorting between electrodes. These requirements contribute tomanufacturing complexity and cost, and can make the connection of thelead to the IMD difficult for the physician.

SUMMARY

In general, the invention is directed to an axial lead connectorassembly for an implantable medical device (IMD). The lead connectorassembly facilitates electrical connection between an implantablemedical lead and circuitry contained within the housing of an IMD. Aconnector header defines an axial stack bore to receive an axial stackof in-line connector components. The connector components define acommon lead bore to receive a proximal end of an implantable lead. Thein-line stack of connector components may include seals, electricalconnector elements, a strain relief, and a locking device, each of whichdefines a passage that forms part of the axial lead bore.

Electrically conductive connector elements are disposed within the axialstack bore at positions corresponding to positions of electricallyconductive lead contacts carried at the proximal end of the lead. Eachconnector element couples one of the lead contacts to a conductor withinthe IMD housing. Each connector element may be integrated with, oradjacent to, a seal device that provides a fluid seal with respect toadjacent connector elements or the outside of the connector header. Anannular strain relief member, mounted in an opening of the axial stackbore, retains the stack of components within the connector header, andreceives the proximal end of the lead. The axial stack of connectorcomponents may be preassembled or pre-fitted for insertion into theaxial stack bore as a unitary stack. Alternatively, the individualconnector components may be inserted serially into the axial stack bore,e.g., one or more components inserted at time.

Each electrical connector element may provide an interference orfriction fit to a respective contact on the lead, enhancing electricalcoupling pressure. Seals may provide a similar interference or frictionfit with the lead body. A locking device, such as a set screw assembly,exerts a lateral force against the lead such that the proximal end ofthe lead resists axial displacement under axial loading forces. Thestrain relief member may support the lead against bending forces. Thelocking device also may be electrically conductive and function as anelectrical connector element for one of the contacts carried by thelead. In some embodiments, a single set screw assembly may be provided.The lead is coupled via the connector header to circuitry within the IMDhousing to deliver electrical stimulation therapy or sense patientconditions.

In one embodiment, the invention provides an implantable medical devicecomprising a connector header defining a first axial bore, and a seriesof electrical connector elements and fluid seals arranged in an axialstack mounted within the first axial bore, wherein the axial stackdefines a second axial bore that extends through the electricalconnector elements and fluid seals to receive a proximal end of animplantable medical lead.

In another embodiment, the invention provides an implantable medicaldevice comprising a connector header defining a first axial bore, and anaxial stack of connector components within the first axial bore, whereinthe axial stack defines a second axial bore extending through thecomponents that receives a proximal end of an implantable medical lead,and wherein the components include electrical connector elements, fluidseals, a locking device that exerts a force to resist displacement ofthe lead, and a strain relief member.

In a further embodiment, the invention provides a method for assemblingan electrical connector assembly for an implantable medical devicecomprising arranging a series of electrical connector elements and fluidseals in an axial stack, and inserting the axial stack into a firstaxial bore defined by a connector header, wherein the axial stackdefines a second axial bore that extends through the electricalconnector elements and fluid seals to receive a proximal end of animplantable medical lead.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an IMD with a lead implantedwithin a patient.

FIG. 2 is a perspective view of an exemplary IMD with an axial leadconnector assembly in conjunction with a lead.

FIG. 3 is an exploded perspective view of an axial lead connectorassembly for an IMD.

FIG. 4 is a block diagram illustrating exemplary functional componentsof an IMD.

FIG. 5 is a side view of the axial lead connector assembly of FIG. 3.

FIG. 6 is a cross-sectional side view of the axial lead connectorassembly of FIG. 3.

FIG. 7 is an enlarged cross-sectional side view of a locking device inthe axial lead connector assembly of FIG. 3.

FIG. 8 is a cross-sectional front view of the locking device of FIG. 7.

FIG. 9 is a top view of the axial lead connector assembly of FIG. 3.

FIG. 10 is a front view of the axial lead connector assembly of FIG. 3.

FIG. 11 is a front view of the axial lead connector assembly of FIG. 3and an IMD housing.

FIG. 12 is an exploded perspective view of the axial lead connectorassembly and the IMD housing.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating an implantable medical device(IMD) 12 having a lead 14 implanted within patient 16. Lead 14 includesone or more electrodes (not shown in FIG. 1) at or near a distal end ofthe lead. As will be described, IMD 12 includes a lead connectorassembly that facilitates electrical connection between lead 14 andcircuitry contained within the housing of an IMD. In accordance with theinvention, the lead connector assembly defines an axial stack bore toreceive an axial stack of in-line connector components. The connectorcomponents together define a common lead bore to receive a proximal endof an implantable lead. The in-line stack of connector components mayinclude seals, electrical connector elements, a strain relief, and oneor more locking devices, each of which defines a passage that forms partof the axial lead bore.

A proximal end of lead 14 carries one or more electrical contacts thatare coupled to respective electrodes via conductors within the body ofthe lead. IMD 12 may be an implantable stimulator that deliverselectrical stimulation to nerve or muscle tissue within patient 16. Forexample, IMD 12 and lead 14 may be configured to deliver electricalstimulation to sacral, pudendal or other pelvic nerves within the pelvicfloor of a patient to alleviate a variety of disorders such as urinaryincontinence, fecal incontinence, constipation, sexual dysfunction,pelvic pain, or other pelvic floor disorders. Lead 14 is sized indiameter and length for any of a variety of nerve or tissue stimulationapplications.

Alternatively, IMD 12 and lead 14 may be configured for spinal cordstimulation, e.g., for chronic pain, or gastric stimulation, e.g., forgastroparesis, obesity or other gastric disorders. As another example,implantable stimulator 12 may provide deep brain stimulation foralleviation of motion disorders, Parkinson's disease, epilepsy, or otherneurological disorders. In those cases, lead 14 may be stereotacticallyprobed into the brain to position electrodes for deep brain stimulationor into the spine for spinal stimulation.

As a further example, IMD 12 may take the form of an implantable cardiacpacemaker that provides therapeutic stimulation to the heart.Alternatively, IMD 12 may take the form of an implantable cardioverteror an implantable defibrillator, or an implantable cardiacpacemaker-cardioverter-defibrillator. IMD 12 may deliver pacing,cardioversion or defibrillation pulses to a patient via electrodesdisposed on a distal end of lead 14. Accordingly, lead 14 may positionelectrodes with respect to various cardiac locations so that IMD 12 candeliver pulses to the appropriate locations.

As a further alternative, IMD 12 may correspond to a patient monitoringdevice that senses physiological parameters, or a device that integratessending and electrical stimulation features. In those cases, lead 14 mayinclude sensors disposed on distal ends of the respective lead forsensing patient conditions. The sensors may comprise electrodes,electrochemical sensors, pressure sensors, flow sensors, acousticsensors, optical sensors, or the like. In many cases, IMD 12 may performboth sensing and stimulation functions. IMD 12 may correspond to any ofa wide variety of medical devices that implement one or more leads andcircuitry coupled to the leads to support stimulation, sensing, or both.

FIG. 2 is a perspective view of an exemplary IMD 12 that includes a lead14. IMD 12 includes a housing 20 that houses IMD circuitry, includingstimulation pulse generation circuitry, power generation circuitry, andtelemetry circuitry. In some embodiments, IMD 12 additionally oralternatively may include sensing circuitry. IMD 12 is coupled to a lead14 via an axial lead connector assembly 22 that receives a proximal end24 of lead 14 to couple lead 14 to the circuitry in housing 20. Housing20, sometimes referred to as a “can,” provides a hermetically sealedenclosure to house an implantable pulse generator (IPG) comprisingsignal processing and/or pulse generating circuitry powered by abattery. Housing 20 is typically formed of a conductive biocompatiblemetal, such as titanium, or a non-conductive biocompatible polymeric orceramic material.

Axial lead connector assembly 22 comprises a connector header formed of,for example, an injection molded dielectric material such aspolyurethane. Connector module assembly 22 defines an elongated axiallead bore 30 to receive a proximal end 24 of lead 14. A distal end 25 oflead 14 includes a plurality of electrodes 29, and the proximal end 24of lead 14 includes a plurality of lead contacts 26A, 26B, 26C, 26D(collectively contacts 26). Lead contacts 26 may be ring contacts.Electrodes 29 may provide stimulation to tissue of patient 14 toalleviate a variety of symptoms or disorders, as discussed above, orsupport electrical sensing. Electrical conductors (not shown) with thebody of lead 14 couple electrodes 29 to respective contacts 26.Electrical feedthrough conductors extend through housing 20 and couplethe electronic circuitry within housing 20 of the IMD 12 with one ormore electrical connector elements within axial lead connector assembly22. The electrical feedthrough conductors may be electrically conductivewires, ribbons, or the like. The electrical connector elements withinconnector assembly 22 electrically and mechanically engage the leadcontacts 26.

Connector module assembly 22 is configured to accommodate a lead 14 withan inline configuration, as shown in FIG. 2, in which a plurality ofelectrical contacts 26 are positioned axially along the length of thelead. In the example of FIG. 2, a strain relief member 28 is providedwithin connector assembly 22. Strain relief member 28 allows lead 14 tobe mechanically connected to connector module assembly 22 using alocking device, such as a set screw assembly. In some embodiments, asingle set screw assembly may be provided, simplifying connection oflead 14 to connector assembly 22. As described in greater detail below,connector assembly 22 incorporates various components, arranged in anaxial, in-line stack, that support simple and reliable electricalcoupling between lead 14 and circuitry in housing 20 while, in someembodiments, reducing overall size of the connector assembly.

FIG. 3 is an exploded perspective view of components that form at leasta part of axial connector assembly 22 for IMD 12. As shown in FIG. 3,connector header 32 includes a grommet aperture 34 that is disposedsubstantially perpendicular to an axial stack bore 33 of connectorheader 32. Axial stack bore 33 receives an axial stack of variouscomponents, including strain relief 28, which defines an axial lead bore30 to receive lead 14. Grommet aperture 34 provides access to axialstack bore 33, and is sized to receive a grommet assembly 36. Grommetassembly 36 is inserted into grommet aperture 34. Grommet assembly 36includes a compression band 79, e.g., made of silicone, and defines anaccess aperture 37 that permits a set screw tool to tighten or loosenset screw 38. At least a portion of grommet assembly 36 may be formedfrom an elastomeric material, such as silicone or polyurethane. When theset screw tightening tool is removed from access aperture 37, grommetassembly 36 closes the access aperture by elastic compression producedby band 36, and thereby self-seals the interior of grommet aperture 34against bodily fluids. A grommet washer 42 retains grommet assembly 36in grommet aperture 34.

A stack of alternating, electrical connector elements 44A, 44B, 44C(collectively 44) and annular electrically insulating inner seals 46A,46B, 46C (collectively 46) is assembled in axial alignment. Eachconnector element 44 may be integrated with, or adjacent to, a seal 46.In the example of FIG. 3, connector elements 44 and seals 46 arecircular. In other embodiments, however, connector elements 44, seals 46and other connector components may have non-circular cross-sections,such as square, rectangular, oval, or triangular cross-sections. As afurther variation, some of connector elements 44 or other connectorcomponents may have U-, C- or V-shaped cross sections, in which caselead 14 extends through a trough defined by such cross-section. Innerseals 46 separate adjacent electrical connector elements 44 from oneanother, and provide a fluid seal between the connector elements.

The stack of connector elements 44 and seals 46 provides an elongatedaxial lead bore 30 sized in diameter and length to receive lead 14. Inparticular, each connector component provides a inner passage orientedalong a common, longitudinal axis to define axial lead bore 30 toreceive lead 14. The position of each connector element 44 correspondsto the position of a respective one of the electrical contacts 26 onlead 14. Each adjacent electrical connector element 44 and inner seal 46may be interlocked or fitted with one another during preassembly of thestack to maintain axial alignment and length and diameter dimensions.Notably, each connector element 44 can be fitted to at least oneadjacent seal 46, without any intervening material from connector header32. Hence, the distances between adjacent components within the axialstack can be reduced or minimized.

Each electrical connector element 44 may be constructed with anelectrically conductive, cylindrical housing having an interiorcircumferential groove or channel that retains an electricallyconductive coil spring element. A distance, or “pitch,” between centerpoints of adjacent connector elements 44 may be approximately equal to apitch between center points of adjacent contacts 26 on lead 14. A springelement in each connector element protrudes slightly into lead bore 30,and is compressed by one of lead contacts 26 when lead 14 is insertedinto the lead bore 30. The spring element exerts a spring force againstthe lead contact 26 to produce enhanced electrical coupling pressurebetween the spring element and the contact.

For example, each contact 26 of lead 14 may have an outer diameter thatis suitably dimensioned to be insertable through the spring element withrelatively low force. The spring then provides a radially inwarddirected spring force on the contact 26. The electrically conductivespring element electrically couples the contact 26 to the electricallyconductive outer housing of the connector element 44. Electricalconnector elements of the type described above are manufactured by BalSeal Engineering Company of Foothill Ranch, Calif. In some embodiments,the spring element may be formed from platinum irridium and the housingof the connector element 44 may be formed from MP35N alloy, which is awell known nickel-cobalt-chromium-molybdenum alloy.

Inner seals 46 may be formed with one or more annular sealing ringsformed in a seal housing. In addition, strain relief member 28 has oneor more inner ring seals (not shown in FIG. 3) to seal against lead body14 and one or more outer ring seals 31 to seal the strain relief member28 against the bore of connector header 32. The outer ring seals 31extend radially outward from an outer diameter of strain relief member28. The inner ring seals associated with strain relief member 28 areshown in FIG. 6. The sealing rings associated with inner seals 46, asshown in FIG. 3, may have an inner diameter slightly smaller than leadbore 30 so that the rings protrude slightly into the bore and arethereby compressed by the outer diameter of lead 14 as the lead slideswithin the bore. Secure, frictional electrical and mechanical contact ismade between lead contacts 26 and electrical connector elements 44,while inner seals 46 seal the electrical connections from fluid ingressthat could cause electrical shorting. As mentioned above, a housing ofeach electrical connector element 44, as well as a spring elementcarried by the connector element, may be made from MP35N alloy.Alternatively, the spring element may be formed from a differentmaterial such as platinum iridium. Seals 46 may be made, for example,from silicone.

The axial stack formed by electrical connector elements 44 and innerseals 46 may further include a locking device, such as set screwassembly 40, located at one end of the stack, as well as strain relief28. This axial stack may be preassembled or fitted together as a unitarystack, and then inserted a unitary stack into axial stack bore 33 ofconnector header 32. Alternatively, the components of the axial stackmay be inserted in series one after the other, or in groups, accordingto their order of placement within axial stack bore 33. In either case,there is no need to overmold the connector header over the components ofthe stack, or consume header space between components. Instead, thecomponents can be stacked one after the other, with no header materialseparating the components, promoting size reduction.

In addition, there is no need to insert the components of the axialstack laterally into header 32. Instead, all components can be axiallyinserted through a single entry hole defined by axial stack bore 33, andthen staked in placed by a strain relief washer 48, as will bedescribed. In some embodiments, header 32 may be constructed such thatthere are no apertures to permit lateral insertion of the components ofthe axial stack. The inner diameter of axial stack bore 33 may varyalong its length. In addition, the cross-section of axial stack bore 33,perpendicular to bore length, may not be circular along its entirelength.

Set screw assembly 40 may be a single set screw assembly. In otherembodiments, two or more set screw assemblies may be provided. However,a single set screw assembly 40 offers reduced complexity and ease ofconnection of lead 14 to connector assembly 22. Set screw assembly 40has a connector element bore that is axially aligned with and part ofthe lead bore 30 and receives inner seal 46A. Inner seal 46A includes aproximal lip 47 that is received by the bore of set screw assembly 40, aridge 49 and a distal lip 51 that is received by seal 44A. Inner seals46B and 46C are similarly arranged. However, inner seals 46B and 46C mayhave a longer axial length than seal 44A, and include an additionalridge.

Set screw assembly 40 also has a set screw bore 53 that is transverse tothe connector element bore and contains a set screw 38 adapted to betightened against a segment of the body of lead 14 within the connectorelement bore. Before the axial stack of connector components is insertedinto connector header 32, set screw 38 may be positioned in set screwassembly 40 by turning clockwise downward until set screw 38 is fullyembedded within set screw assembly 40. After the stack is inserted intoconnector header 32, set screw 38 may be repositioned by backing setscrew 38 counterclockwise to a given point. In this manner, theconnector element bore within set screw assembly 40 is open to receivelead 14. The set screw 38 may be tightened downward to exert a laterallocking force against a contact 26A carried by lead 14.

Set screw assembly 40 may include a flange 39 that abuts with a stopsurface within axial stack bore 33 of connector header 32 to properlyposition the set screw assembly 40 with respect to grommet aperture 34in the connector header 32. Set screw assembly 40 is positioned foraccess via a window 55A. Set screw 38 and set screw assembly 40 may bemade from an electrically conductive material such as, for example,titanium. Set screw assembly 40 electrically conducts electricalstimulation or sensed potentials between electrical contact 26A and anelectrical conductor, such as a wire, within channel 57A, whichcommunicates with window 55A. Window 55A provides access to couple setscrew assembly 40 and a feedthrough conductor, e.g., a wire, withinchannel 57A, e.g., by welding. As an alternative to set screw assembly40, other types of locking devices may be provided. As an example, a cammechanism alternatively may be provided in which a cam is rotated toextend into lead bore 30 to exert pressure against lead 14.

The axial connector stack may further comprise strain relief member 28,which is coaxially aligned with stack bore 33 and lead bore 30. Strainrelief member 28 may stabilize the proximal portion of lead 14 insertedwithin lead bore 30, thereby preventing stretching, bending or twistingdue to forces applied to the portion of lead 14 remaining outside leadbore 30. Strain relief member 28 may be made from silicone or othersuitable materials. A strain relief washer 48 is located at one end ofthe stack. Strain relief washer 48 may be ultrasonically welded toconnector header 32, thereby staking strain relief member 28 to theconnector header 32 and sealing the junction of lead 14 and lead bore 30without medical adhesive. Strain relief washer 48 may be made, forexample, from polyurethane. As discussed previously, strain reliefmember 28 includes outer ring seals 31 to seal the strain relief member28 against the interior of the bore of connector header 32. In addition,strain relief member 28 includes inner ring seals 35 (FIG. 6) that sealagainst the outer diameter of lead 14. Accordingly, upon insertion, lead14 must have a sufficient insertion force to overcome interferenceforces presented by inner ring seals 35, connector elements 44, andinner ring seals 46.

Each electrical connector element 44, inner seal 46, set screw assembly40, and strain relief member 28 has a predetermined axial length betweenproximal and distal ends thereof, and the combined axial lengths of thetotal number of electrical connector elements 44, inner seals 46, setscrew assembly 40, and strain relief member 28 define the stack length.The stack can be inserted as a unit, or sequentially one after the otheror in groups, into lead bore 30 of connector header 32. When the stackassembly is completed, the stack is fitted into the axial stack bore 33of connector header 32. When the fitting assembly is complete,electrical connector elements 44A, 44B and 44C are positioned withinlateral windows 55B, 55B, 55D, respectively, for connection withfeedthrough wires extending within channels 57B, 57C and 57D,respectively, for electrical connection to circuitry within IMD housing20. Windows 55A, 55B, 55C provide access to electrically connectconnector elements 44A, 44B, 44C to wires within respective channels57B, 57C, 57D, e.g., by welding.

Upon insertion of lead 14, contacts 26B, 26C, 26D reside withinconnector elements 44A, 44B and 44C of the axial stack. Contact 26A isnot received within a connector element. Instead, contact 26A isreceived at a position within set screw assembly 40. Set screw 38 thenbiases contact 26A downward to hold lead 14 in place and promoteelectrical contact between contact 26A and the electrically conductiveset screw assembly 40. Hence, lead 14 includes N electrically conductivecontacts, but there are only N−1 connector elements 44A, 44B and 44Cdisposed at positions corresponding to the N−1 most proximal contacts26B, 26C, 26D. The screw assembly 40 is positioned such that the setscrew 38 exerts a lateral force against the most distal contact carriedat the proximal end of the lead 14, i.e., contact 26A.

In operation, a physician inserts the proximal end 24 of lead 14 intolead bore 30 with sufficient force to overcome the insertion forcespresented by the springs within connector elements 44A, 44B and 44C andthe frictional forces presented by the inner diameters of inner seals46A, 46B and 46C. The proximal end 24 of lead 14 passes through strainrelief member 28 and extends into lead bore 30 so that lead contacts 26carried by proximal end 24 are brought into alignment with respectiveconnector elements 44 and feedthrough channels 57, which creates anelectrical interconnection.

As will be described in further detail below with respect to FIGS. 6 and7, grommet assembly 36 is disposed within grommet aperture 34. Grommetassembly 36 defines an access aperture 37 to enable rotation of the setscrew 38 within grommet aperture 34. In particular, a tool such as atorque wrench or hex wrench may be inserted into access aperture 37 totighten set screw 38 against or to loosen set screw 38 from a leadcontact 26 of lead 14 received in lead bore 30. Tightening set screw 38may exert a lateral force against the lead 14 such that the proximal end24 of the lead 14 resists axial displacement under axial loading forces,and may further inhibit retraction of lead 14 from lead bore 30. Agrommet washer 42 retains grommet assembly 36 within grommet aperture34. Grommet washer 42 may be made from polyurethane.

Electrical conductors or feedthrough conductors, e.g., such as an arrayof preformed niobium ribbons, connected at one end to circuitry withinhousing 20, are inserted into feedthrough channels 57 of connectorheader 32. The free ends of the electrical conductors may be welded,e.g., by parallel gap welding, to electrical connector elements 44A,44B, 44C of the stack for connection with contacts 26B, 26C, 26D,respectively, and to a set screw assembly 40 for connection with contact26A. The electrical conductors in feedthrough channels 57 connectelectrical connector elements 44 and set screw assembly 40 to circuitryof the IMD housed within housing 20. The portion of the axial stackexposed by windows 55 may be over-molded with an elastomeric compound,e.g., silicone or silicone adhesive or other polymers, to fill theremaining space of axial stack bore 33 and present a finished outersurface.

The arrangement components illustrated in FIG. 3 can provide a number ofadvantages. For example, because a connector housing wall is notrequired between each electrical connector 44 and inner seal 46,successive electrical connectors 44 can be placed close to one another.In other words, the pitch or “spacing” between adjacent lead contacts 26disposed axially along the lead tip can be reduced, permitting anincreased density of electrical interconnections. Accordingly, thisfeature is particularly useful for in-line lead systems in which medicallead 14 includes a number of electrical lead contacts disposed alongaxial positions of the lead. Although four electrical contacts 26 areshown in the figures, the axial stack described herein may beparticularly useful with leads carrying greater numbers of contacts,such as eight or sixteen contacts.

FIG. 4 is a block diagram illustrating exemplary functional componentsof IMD 12. In the example of FIG. 4, IMD 12 may include a processor 50,memory 52, power source 54, telemetry module 56, pulse generator 58 andelectrodes 60A-60D. Telemetry module 56 is optional and may permitcommunication with an external controller for transfer of data andadjustment of stimulation parameters. Processor 50 controls operation ofIMD 12 and may include one or more microprocessors, digital signalprocessors (DSPs), application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), or other digital logiccircuitry.

Memory 52 may include any magnetic, electronic, or optical media, suchas random access memory (RAM), read-only memory (ROM),electronically-erasable programmable ROM (EEPROM), flash memory, or thelike. Memory 52 may store program instructions that, when executed byprocessor 50, cause the processor to perform various functions tosupport delivery of electrical stimulation, processing of sensed signalsor telemetry. For example, memory 52 may store instructions forprocessor 50 to execute in support of control of telemetry module 56 andpulse generator 58.

Telemetry module 56 may include a transmitter and receiver to permitbi-directional communication between IMD 12 and an external controller.In this manner, external controller 24 may transmit commands to IMD 12and receive status and operational information from the stimulationdevice. Telemetry module 56 includes an antenna 62, which may take avariety of forms. For example, antenna 62 may be formed by a conductivecoil or wire embedded in a housing 20 associated with IMD 12.Alternatively, antenna 62 may be mounted on a circuit board carryingother components of IMD 12, or take the form of a circuit trace on thecircuit board. If IMD 12 does not include a telemetry module 56, amagnetic reed switch may be provided in a circuit between power source54 and the other components of the device so that, with the aid of anexternal magnet, the device may be turned on at the time the device isplaced in the patient. Alternatively, IMD 12 may simply be activatedupon release from an endoscopic delivery device.

Power source 54 may take the form of a battery and power circuitry. Thebattery may be a non-rechargeable, e.g., primary, battery. The batterymay take the form of any of a variety of lithium-ion batteries wellknown in the implantable medical device arts. Different types ofbatteries or different battery sizes may be used, depending on therequirements of a given application. In further embodiments, powersource 54 may be rechargeable via induction or ultrasonic energytransmission, and include an appropriate circuit for recoveringtranscutaneously received energy. For example, power source 54 mayinclude a secondary coil and a rectifier circuit for inductive energytransfer. In still other embodiments, power source 54 may not includeany storage element, and IMD 12 may be fully powered via transcutaneousinductive energy transfer.

Pulse generator 58 produces an electrical stimulation pulses withparameters, such as voltage or current amplitude, pulse width, pulserate, and duty cycle, selected to alleviate particular symptoms orprovide particular therapy. As shown in FIG. 4, pulse generator 58includes a charging circuit 64, an energy storage device 66, and astimulation interface 68. Charging circuit 64 converts energy suppliedby power source 54 to charge energy storage device 66, which may be acapacitor. Stimulation interface 68 amplifies and conditions charge fromenergy storage device 66 to produce an electrical stimulation waveformfor application to electrodes 60A-60D, which are carried by a lead suchas lead 14. As an example, pulse generator 58 may incorporate circuitrysimilar to the pulse generation circuitry in the ITREL 3neurostimulator, commercially available from Medtronic, Inc. ofMinneapolis, Minn.

FIG. 5 is a side view illustrating connector assembly 22 in greaterdetail. As shown in FIG. 5, feedthrough channels 57 and windows 55 areformed in one side of connector header 32. Electrical feedthroughconductors (not shown) are inserted into feedthrough channels 57 ofconnector header 32. The free ends of the electrical conductors may beparallel-gap welded to electrical connector elements 44 and set screwassembly 40 within connector module assembly 22 via windows 55. Windows55 allow manufacturing operators to view the welding process, and mayinclude one or more ramped or chamfered surfaces that taper outward froma narrower space at an internal weld point to the larger weld window.With a chamfer, the internal weld point may be more visible andaccessible. A chamfered surface is illustrated in more detail in FIG. 8.

Connector header 32 may further include a cavity 72 for receiving aradio-opaque identifier tag (not shown) for identification of the IMD,e.g., by model number, serial number, stimulation or sensingcapabilities, or the like. In the example of FIG. 5, cavity 72 includesa fastening hole 74 for fastening the radio-opaque identifier tag tocavity 72. Connector header 32 also includes holes 76 formed at a baseof connector header 32 for attaching connector assembly 22 to housing20, as will be discussed in further detail with respect to FIG. 12. Ingeneral, after attachment of connector assembly 22 to housing 20, aphysician simply inserts lead 14 into axial lead bore 30 defined by theaxial stack of components, and tightens set screw 38 to hold theproximal end of lead 14 in place within the connector assembly.

FIG. 6 is a cross-sectional side view of connector module assembly 22 ofFIG. 5. As shown in FIG. 6, grommet assembly 36 is disposed withingrommet aperture 34 to enable insertion of a tool, such as a torquewrench or hex wrench, for rotation of set screw 38. The tool is insertedvia access aperture 37 and serves to tighten set screw 38 against or toloosen set screw 38 from contact 26A of lead 14 received in lead bore 30of set screw assembly 40. Grommet assembly 36 is retained withinconnector header 32 by grommet washer 42. Set screw assembly 40 mayinclude a flange 39 that abuts a stop 73 within the interior axial stackbore 33 of connector header 32. Stop 73 may be molded into connectorheader 32. Stop 73 and flange 39 serve to properly position set screw 38and set screw assembly 40 with respect to grommet aperture 34 inconnector header 32, and with respect to window 55A for connection ofthe electrically conductive set screw assembly 40 to a feedthrough wirewithin channel 57A.

When the in-line stack comprising electrical connector elements 44,inner seals 46, set screw assembly 40, and strain relief 28 is insertedinto axial stack bore 33 of connector header 32, flange 39 abuts stop73, thereby preventing the stack from being inserted beyond a certainpoint into axial stack bore 33. In this manner, set screw 38 is properlyaligned with grommet aperture 34 within connector header 32 and, moreparticularly, access aperture 37 in grommet assembly 36. Strain reliefwasher 48 is then ultrasonically welded to connector header 32 at theopening of recess 45 to seal the stack within connector header 32.

As shown in FIG. 6, strain relief 28 further includes inner ring sealmembers 35 which protrude into lead bore 30 for interference with lead14. Inner ring seal members 35 provide a substantial fluid seal againstlead 14, while outer ring seal members 31 provides a substantial fluidseal against the interior axial stack bore 33 of connector header 32.Strain relief 28, including seals 31 and seals 35, may be integrallymolded, e.g., from silicone. Upon implantation, the proximal end of lead14 is inserted up to the point that the proximal end abuts a stop 75within connector header 32, at which point contact 26A is aligned withset screw assembly 40 and contacts 26B, 26C, 26D are aligned withrespective connector elements 44A, 44B, 44C.

Portion A of FIG. 6 illustrates components within grommet aperture 34 ofconnector header 32. Portion A is enlarged and illustrated in furtherdetail in FIG. 7. In particular, FIG. 7 is a cross-sectional side viewof grommet assembly 36 and set screw 38. Grommet assembly 36 provides anaccess aperture 37 that permits access of a set screw tightening deviceto engage a socket 80 of set screw 38 for enabling rotation of set screw38 within set screw assembly 40. FIG. 8 is a cross-sectional front viewof grommet assembly 36 of FIG. 7.

Socket 80 may be a slot, a star, a hexagon, or any other shape. A mainbody of set screw 38 is threaded for engagement with a threaded setscrew bore 53. At implantation, the proximal end 24 of lead 14 isinserted into lead bore 30 of connector module 22 to locate contact 26Awithin set screw assembly 40. A set screw tightening tool, e.g., a hexwrench or torque wrench, may be inserted through grommet washer 42 andgrommet assembly 36 into access aperture 37 to engage a socket in setscrew 38. By rotating the tightening tool, set screw 38 tightens againstan inner surface of set screw assembly 40 and ensures electrical contactbetween contact 26A of lead 14 and the circuitry within housing 20, viathe electrically conductive set screw assembly 40 and the feedthroughwire within channel 57A.

In some embodiments, grommet assembly 36 may be formed from silicone,polyurethane or other soft elastomeric material. In the example of FIGS.6-8, grommet assembly is formed from a first half grommet 77A and asecond half grommet 77B, which are held together by a ring-like,compressive band 79 that extends around a periphery of the half grommets77A, 77B. An interface 88 between the half grommets 77A, 77B defines theaccess aperture 37, which is normally closed due to the compressive biasapplied by band 79. Band 79 may be formed from an elastomeric material,such as silicone. With the compressive force applied by band 79, accessaperture 37 forms a self-sealing slit through which a tool can beinserted to access set screw 38.

A ring of adhesive may be provided around a top surface of grommetassembly 36. Outer, lower surfaces of grommet assembly 36 seal against alower, smaller diameter portion of grommet 34 aperture, eliminating theneed for the adhesive. For example, grommet aperture 34 may include ashelf and smaller diameter portion near the bottom of the aperture thatcompresses and seals against a bottom portion 82 of grommet assembly 36,which may be more flexible. The sealing pressure between the bottomportion 82 of grommet assembly and the reduced diameter wall of grommetaperture 34 may result in less “push-back” of grommet assembly 36against grommet aperture 34, which may reduce relaxation of the materialforming connector header 32 and subsequent reduction in sealingperformance.

In some embodiments, as shown in FIG. 7, grommet aperture 34 may includea tapered diameter or conical shape such that the inner sealing surfacesof the grommet assembly 36 at interface 88 are minimally compressed bythe grommet aperture 34, which may reduce permanent sealing of thesealing surfaces and possible damage and reduced sealing performanceafter tool insertion and removal. For example, grommet aperture 34 mayinclude a smaller diameter section 91 at the bottom of the aperture anda larger diameter section 93 that tapers from the smaller diameteradjacent small diameter section 91 to a larger diameter near grommetwasher 42. As also shown in FIG. 7, an outer diameter of grommetassembly 36 is larger than an inner diameter of washer 42, therebyserving to retain the grommet assembly within connector head 32. Also,the outer diameter of set screw 38 may be larger than an inner diameterof the channel 90 between set screw 38 and grommet assembly 36. Theshape of grommet aperture 34 and channel 90 is further sized such that awrench may access socket 80 of set screw 38, but set screw 38 cannot bebacked out into grommet aperture 34. This may eliminate set screw 38from “wandering” out of set screw assembly 40.

FIG. 8 provides a cross-sectional front view of connector header 32,from a direction looking into axial lead bore 30. FIG. 8 furtherillustrates a chamfered surface 85 within windows 57. Window 57A, forexample, has a generally flat surface 83 that extends outward from aweld point between set screw assembly 40 and a feedthrough conductor 98.In some embodiments, however, a chamfered surface 85 may be provided, asillustrated in dashed lines. The chamfered surface 85 ramps downward ina tapered manner from a narrower space proximate the weld point to alarger space that defines the weld window for access by a technician. Inthis manner, the cross-sectional surface area in a direction lookinginto window 57A increases from a smaller cross-sectional surface areaproximate the weld point between conductor 98 and set screw assembly 40to a larger cross-section surface area at the outer entrance of thewindow. With a chamfered surface 85, the internal weld point may be morevisible and accessible. One of more surfaces defining window 57 may bechamfered. For example, window 57 may be chamfered on one side, twosides, or all sides. In addition, each of windows 57A-57D may include atleast one chamfered surface 81.

FIG. 9 is a top view of connector module assembly 22. As shown in FIG.9, the top of half grommets 77A, 77B and the access aperture 37 formedby the interface between the half-grommets can be viewed through anopening of grommet washer 42. A tightening tool, e.g., a torque wrenchor a hex wrench, may be inserted through access aperture 37 of grommetassembly 36 to rotate and tighten set screw 38 against a lead contact 26of lead 14.

FIG. 10 is a front view of connector module assembly 22. FIG. 11 is afront view of lead connector assembly 22 and the IMD housing 20. As canbe seen from FIGS. 9-11, a portion of strain relief member 28 extendsoutside of connector header 32. Strain relief washer 48 has an innerdiameter that is smaller than a diameter of a portion of strain reliefmember 28 within axial stack bore 33, thereby retaining strain relief 28within connector header 32. In particular, strain relief washer 48 maybe ultrasonically welded to connector header 32 to hold the stackcontaining strain relief member 28 in place within connector header 32.Strain relief washer 48 seals the portion of strain relief member 28having a larger diameter than strain relief washer 48 within axial stackbore 33 of connector header 32. Also shown in FIGS. 10 and 11 is axiallead bore 30, where lead 14 may be inserted into connector moduleassembly 22.

FIG. 12 is an exploded perspective view of connector module assembly 22and housing 20. Connector module assembly 22 is connected to housing 20by a pin and strap mechanism. In particular, four holes 76 are formed atthe base of connector header 32 (only two of which are visible in FIG.12). Connector module assembly 22 is placed upon housing 20 such thatholes 76 align with straps 94 of housing 20. Pins 96 are insertedthrough straps 94 and into holes 76 to secure connector module assembly22 to housing 20. An adhesive may additionally be used to secureconnector module assembly 22 to housing 20. Such an adhesive may providemechanical strength to the connection between connector module assembly22 and housing 20, and also may provide a barrier preventing fluidingress to the area between connector module assembly 22 and housing 20.

Electrical feedthrough wires 98 are connected inside housing 20 toelectronic circuitry of an IPG within housing 20. Ferrules 99 arepresent where electrical feedthrough wires 98 emerge from housing 20.The point at which electrical feedthrough wires 98 emerge from housing20 may be filled with encapsulant. When connector module assembly 22 issecured to housing 20, electrical feedthrough wires 98 are inserted intofeedthrough channels 57 of connector header 32. The free ends ofelectrical feedthrough wires 98 are parallel-gap welded to electricalconnector elements 44 and set screw assembly 40, as applicable, withinconnector module assembly 22.

Connector header 32 has a cavity 72 formed therein for receivingradio-opaque identifier tag 100. Cavity 72 includes a fastening hole 74for fastening radio-opaque identifier tag 100 to radio-opaque cavity 72.Radio-opaque identifier tag 100 may have a code for identification ofthe IMD. Radio-opaque identifier tag 100 may be made of a radio-opaquemetal, e.g., tungsten.

An elastomeric compound, e.g., silicone rubber or silicone adhesive orother polymers, is injected within connector module assembly 22 to fillthe remaining space of axial stack bore 33 and present a finished outersurface. The elastomeric compound is injected until the elastomericcompound is visible flowing out of feedthrough channels 57. Radio-opaqueidentifier tag 100 may be readable through the adhesive via X-ray.

Although described for purposes of illustration as having four leadcontacts 26 and four corresponding electrical terminals in the form ofconnector elements 44 and set screw assembly 40, the invention may beimplemented with a different amount of lead contacts and electricalconnection elements, e.g., eight. The eight lead contacts and electricalconnection elements may be located axially in-line, or connector header32 may include two bores, e.g., with four axially aligned contacts each.To overcome the increased frictional force associated with an increasednumber of electrical connection elements disposed axially withinconnector header 32, lead 14 may be a variable diameter lead. Inparticular, lead 14 may taper from a narrower diameter at the proximaltip to a larger diameter at a position away from the proximal tip, e.g.,coincident with electrical contact 26A.

The dimensions of the various components described herein may varyaccording to different applications or design considerations. Thefollowing dimensions are exemplary and should not be considered limitingof the invention as broadly embodied and described herein. In anexemplary embodiment, lead 14 may have an outer diameter ofapproximately 1 mm to 2 mm, strain relief washer 48 may have an innerdiameter of approximately 2 mm to 5 mm, strain relief 28 may have aninner diameter of approximately 1 mm to 2 mm and an outer diameter ofapproximately 3.5 mm to 6 mm. However, a portion of strain relief 28passing through strain relief washer 48 will have an outer diameterslightly smaller than the inner diameter of the strain relief washer.Outer ring seals 31 may define approximately an additional 0.25 mm to 1mm beyond the outer diameter of the strain relief, and inner ring seals35 may define approximately an additional 0.25 mm to 1 mm beyond theinner diameter of the strain relief. The inner diameter of strain relief28 generally defines the diameter of axial lead bore 30, and issubstantially common among the stack components.

Grommet washer 42 may have an inner diameter of approximately 2 mm to 4mm, and grommet assembly 36 may have an outer diameter of approximately4 mm to 5 mm. Grommet aperture 34 may have a minimum diameter ofapproximately 3.5 mm to 4.5 mm, a maximum diameter of approximately 4.5mm to 6 mm (i.e., at the maximum extent of the tapered or conicalregion), and a depth of approximately 2.5 mm to 4 mm. Electricalconnector elements 44 may each have an inner diameter approximatelyequal to the diameter of axial lead bore 30, and an outer diameter ofapproximately 2 mm to 4 mm. Inner seals 46 may have an inner diameterslightly smaller than the diameter of axial lead bore 30 and an outerdiameter of approximately 2.2 mm to 5 mm. The overall length of thestack of components, e.g., strain relief 28, set screw assembly 40,connector elements 44 and seals 46, along the length of axial lead bore30, may be in a range of approximately 22 mm to 35 mm.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

1. An implantable medical device comprising: a connector header defininga first axial bore and comprising a stop surface within the first axialbore; and a series of electrical connector elements, fluid seals, and alocking device arranged in an axial stack mounted within the first axialbore, wherein the axial stack defines a second axial bore that extendsthrough the electrical connector elements, fluid seals, and the lockingdevice, wherein the second axial bore is configured to receive aproximal end of an implantable medical lead, wherein the locking deviceexerts a lateral force against the lead such that the proximal end ofthe lead substantially resists axial displacement under axial loadingforces, wherein the locking device is positioned within the axial stackat a position distal to at least one of the electrical connectorelements, wherein the first axial bore comprises an axial opening thatis configured to axially receive the electrical connector elements,fluid seals, and locking device when the electrical connector elements,fluid seal, and locking device are axially inserted, wherein the lockingdevice includes a flange that engages the stop surface to position thelocking device, and wherein the locking device is electricallyconductive and is disposed within the second axial bore at a positioncorresponding to an electrically conductive contact carried by theproximal end of the lead.
 2. The device of claim 1, wherein theelectrical connector elements are disposed at positions corresponding toelectrically conductive contacts carried by the proximal end of thelead, and some of the fluid seals are disposed between adjacentelectrically conductive contacts.
 3. The device of claim 1, wherein thelocking device includes a set screw assembly with a set screw that isrotatable to extend into the second axial bore and exert the lateralforce against the lead, wherein the set screw assembly is electricallyconductive.
 4. The device of claim 3, wherein the lead includes Nelectrically conductive contacts, the connector elements include N−1connector elements disposed at positions corresponding to the N−1 mostproximal contacts carried at the proximal end of the lead, and the setscrew assembly is positioned to exert a lateral force against the mostdistal electrically conductive contact carried at the proximal end ofthe lead.
 5. The device of claim 3, wherein the set screw assembly is asingle set screw assembly.
 6. The device of claim 3, further comprising:a grommet aperture defined within the connector header perpendicular tothe first axial bore, wherein the grommet aperture provides access tothe first axial bore; and a grommet assembly within the grommetaperture, wherein the grommet assembly defines a self-sealing accessaperture that permits insertion of a tool to tighten the set screwagainst one of the lead contacts of the lead.
 7. The device of claim 6,wherein the grommet aperture has a cross-section with a first diametersized to compress the grommet assembly, and a second diameter largerthan the first diameter.
 8. The device of claim 1, further comprising astrain relief member arranged in the axial stack, wherein the secondaxial bore extends through the strain relief member, and a fixationmember coupled to the strain relief member to retain the axial stackwithin the first axial bore.
 9. The device of claim 1, wherein each ofthe connector elements includes a spring element that exerts an inwardforce against one of the contacts.
 10. The device of claim 1, furthercomprising a plurality of lateral windows that permit lateral access tothe connector elements to couple feedthrough conductors to the connectorelements, wherein each of the windows defines at least one chamferedsurface.
 11. The device of claim 1, wherein adjacent components in theaxial stack are in substantially direct contact with one another.
 12. Animplantable medical device comprising: a connector header defining afirst axial bore and comprising a stop surface within the first axialbore; and an axial stack of connector components within the first axialbore, wherein the axial stack defines a second axial bore extendingthrough the components that is configured to receive a proximal end ofan implantable medical lead, wherein the components include electricalconnector elements, fluid seals, a locking device that exerts a force toresist displacement of the lead, and a strain relief member, wherein thelocking device is positioned within the axial stack at a position distalto at least one of the electrical connector elements, wherein the firstaxial bore comprises an axial opening that is configured to axiallyreceive the axial stack when the axial stack is axially inserted, andwherein the locking device includes a flange that engages the stopsurface to position the locking device.
 13. The device of claim 12,wherein the electrical connector elements are disposed at positionscorresponding to electrically conductive contacts carried by theproximal end of the lead, and some of the fluid seals are disposedbetween adjacent electrically conductive contacts.
 14. The device ofclaim 13, wherein the locking device is electrically conductive and isdisposed within the second axial bore at a position corresponding to anelectrically conductive contact carried by the proximal end of the lead.15. The device of claim 14, wherein the locking device includes a setscrew assembly with a set screw that is rotatable to extend into thesecond axial bore and exert the lateral force against the lead, whereinthe set screw assembly is electrically conductive.
 16. The device ofclaim 15, further comprising: a grommet aperture defined within theconnector header perpendicular to the first axial bore, wherein thegrommet aperture provides access to the first axial bore; and a grommetassembly within the grommet aperture, wherein the grommet assemblydefines a self-sealing access aperture that permits insertion of a toolto tighten the set screw against one of the lead contacts of the lead.17. The device of claim 16, wherein the grommet aperture has across-section with a first diameter sized to compress the grommetassembly, and a second diameter larger than the first diameter.
 18. Thedevice of claim 12, further comprising a fixation member coupled to thestrain relief member to retain the axial stack within the first axialbore.
 19. The device of claim 12, further comprising a plurality oflateral windows that permit lateral access to the connector elements tocouple feedthrough conductors to the connector elements, wherein each ofthe windows defines at least one chamfered surface.
 20. The device ofclaim 12, wherein adjacent components in the axial stack are insubstantially direct contact with one another.
 21. An implantablemedical device comprising: a connector header defining a first axialbore and comprising a stop surface within the first axial bore; a seriesof electrical connector elements, fluid seals, a locking device, and astrain relief member arranged in an axial stack mounted within the firstaxial bore, wherein the axial stack defines a second axial bore thatextends through the electrical connector elements, fluid seals, thelocking device, and the strain relief member; and a fixation membercoupled to the strain relief member to retain the axial stack within thefirst axial bore, wherein the second axial bore is configured to receivea proximal end of an implantable medical lead, wherein the lockingdevice exerts a lateral force against the lead such that the proximalend of the lead substantially resists axial displacement under axialloading forces, wherein the locking device is positioned within theaxial stack at a position distal to at least one of the electricalconnector elements, wherein the first axial bore comprises an axialopening that is configured to axially receive the electrical connectorelements, fluid seals, and locking device, and wherein the lockingdevice includes a flange that engages the stop surface to position thelocking device when the electrical connector elements, fluid seal, andlocking device are axially inserted.
 22. A method for assembling anelectrical connector assembly for an implantable medical devicecomprising: arranging a series of electrical connector elements, fluidseals, and a locking device in an axial stack; and axially inserting theaxial stack into a first axial bore defined by a connector header,wherein the axial stack defines a second axial bore that extends throughthe electrical connector elements, fluid seals, and the locking deviceto receive a proximal end of an implantable medical lead, whereinaxially inserting the axial stack comprises axially inserting the axialstack into the first axial bore such that the locking device ispositioned within the axial stack at a position distal to at least oneof the electrical connector elements, wherein the locking device isconfigured to exert a lateral force against the lead such that theproximal end of the lead substantially resists axial displacement underaxial loading forces, wherein the locking device includes a flange,wherein axially inserting the axial stack includes axially inserting theaxial stack into the first axial bore until the flange engages a stopsurface of the connector header to position the locking device, whereinthe locking device includes a set screw assembly with a set screw thatis rotatable to extend into the second axial bore and exert the lateralforce against the lead, and wherein the set screw assembly iselectrically conductive.
 23. The method of claim 22, wherein arrangingincludes arranging the electrical connector elements at positionscorresponding to electrically conductive contacts carried by theproximal end of the lead, and arranging some of the fluid seals aredisposed between adjacent electrically conductive contacts.
 24. Themethod of claim 23, further comprising attaching the electricalconnector elements to feedthrough conductors associated with theimplantable medical device via lateral windows, wherein each of thewindows defines at least one chamfered surface.
 25. The method of claim23, wherein arranging includes arranging adjacent components in theaxial stack so that the components are in substantially direct contactwith one another.
 26. The method of claim 22, wherein the locking deviceis electrically conductive, and arranging further includes arranging thelocking device in the axial stack at a position corresponding to anelectrically conductive contact carried by the proximal end of the lead.27. The method of claim 22, wherein the lead includes N electricallyconductive contacts, and the connector elements include N−1 connectorelements disposed at positions corresponding to the N−1 most proximalcontacts carried at the proximal end of the lead, and arranging includesarrange the set screw assembly at a position in the lateral stack toexert a lateral force against the most distal electrically conductivecontact carried at the proximal end of the lead.
 28. The method of claim22, wherein arranging includes arranging a single set screw assembly inthe axial stack.
 29. The method of claim 22 further comprising insertinga grommet assembly into a grommet aperture defined within the connectorheader perpendicular to the first axial bore, wherein the grommetaperture provides access to the first axial bore, and wherein thegrommet assembly defines a self-sealing access aperture that permitsinsertion of a tool to tighten the set screw against one of the leadcontacts of the lead.
 30. The method of claim 29, wherein the grommetaperture has a cross-section with a first diameter sized to compress thegrommet assembly, and a second diameter larger than the first diameter.31. The method of claim 22, further comprising inserting the proximalend of the lead into the second axial bore, and actuating the set screwto lock the lead within the second axial bore.
 32. The method of claim22, wherein arranging further includes arranging a strain relief memberin the axial stack, wherein the second axial bore extends through thestrain relief member, the method further comprising coupling a fixationmember to the strain relief member to retain the axial stack within thefirst axial bore.
 33. A method for assembling an electrical connectorassembly for an implantable medical device comprising: arranging aseries of electrical connector elements, fluid seals, and a lockingdevice in an axial stack; and axially inserting the axial stack into afirst axial bore defined by a connector header, wherein the axial stackdefines a second axial bore that extends through the electricalconnector elements, fluid seals, and the locking device to receive aproximal end of an implantable medical lead, wherein axially insertingthe axial stack comprises axially inserting the axial stack into thefirst axial bore such that the locking device is positioned within theaxial stack at a position distal to at least one of the electricalconnector elements, wherein the locking device is configured to exert alateral force against the lead such that the proximal end of the leadsubstantially resists axial displacement under axial loading forces,wherein the locking device includes a flange, wherein axially insertingthe axial stack includes axially inserting the axial stack into thefirst axial bore until the flange engages a stop surface of theconnector header to position the locking device, and wherein the lockingdevice is electrically conductive, and arranging further includesarranging the locking device in the axial stack at a positioncorresponding to an electrically conductive contact carried by theproximal end of the lead.
 34. A method for assembling an electricalconnector assembly for an implantable medical device comprising:arranging a series of electrical connector elements, fluid seals, alocking device, and a strain relief member in an axial stack; axiallyinserting the axial stack into a first axial bore defined by a connectorheader; and coupling a fixation member to the strain relief member toretain the axial stack within the first axial bore, wherein the axialstack defines a second axial bore that extends through the electricalconnector elements, fluid seals, the locking device, and the strainrelief member to receive a proximal end of an implantable medical lead,wherein axially inserting the axial stack comprises axially insertingthe axial stack into the first axial bore such that the locking deviceis positioned within the axial stack at a position distal to at leastone of the electrical connector elements, wherein the locking device isconfigured to exert a lateral force against the lead such that theproximal end of the lead substantially resists axial displacement underaxial loading forces, and wherein the locking device includes a flange,wherein axially inserting the axial stack includes axially inserting theaxial stack into the first axial bore until the flange engages a stopsurface of the connector header to position the locking device.